1. Field of the Invention
The present invention relates generally to a plasma display panel, and more particularly, to a method of driving a plasma display panel for improving contrast by minimizing the quantity of luminescence during a non-luminescent display period, that is, a reset period.
2. Description of the Prior Art
A plasma display panel (hereinafter, PDP) displays images including characters or graphics by making UV lights of 147 nm, which is produced in a non-active mixed gas discharge of He+Xe or Ne+Xe, hit phosphor and radiate. In this PDP, super thin and light structure is easily achieved, and greatly enhanced image can be provided by recent technology development. Particularly, in three electrodes AC normal radiation type PDP, because wall electric charges are accumulated at a surface in discharge and electrodes are protected from sputtering due to discharge, there is an advantage of low voltage driving and longevity.
FIG. 1 is a perspective view showing a conventional AC normal radiation PDP.
As shown in FIG. 1, a discharge cell of three electrodes AC normal radiation type PDP includes a scanning electrode 12Y and a sustain electrode 12Z formed on an upper substrate, and an address electrode 20X formed on an under substrate.
An upper dielectric layer and a protection layer are formed on the upper substrate which has the scanning electrode 12Y and the sustain electrode 12Z formed in order thereon. Wall electric charges produced in plasma discharge are accumulated in the upper dielectric layer 14. The protection layer 16 not only protects damage of the upper dielectric layer 14 from sputtering in plasma discharge but also improves production efficiency of secondary electron. Conventionally, an MgO is used as the protection layer 16. An under dielectric layer 22 and a barrier rib 24 are formed on the under substrate 18 having the address electrode 20X formed thereon, and a phosphor 26 is applied to surfaces of the under dielectric layer 22 and the barrier rib 24. The address electrode 20X is formed in a direction crossing the direction of the scanning electrode 12Y and the sustain electrode 12Z.
The barrier rib 24 is formed in order with the address electrode 20X, and protects UV lights and visible lights produced in discharge from leakage to adjacent cells. The phosphor 26 is excited by UV lights produced in plasma discharge, and then produces any one visible light of red, green, and blue. Non-active gas is injected into a discharge space between the upper and under electrodes 10, 18 and the barrier rib 24 for gas discharge.
Such discharge cells are arranged in a matrix form, as shown in FIG. 2. As shown in FIG. 2, a discharge cell 1 is formed over an area where a scanning electrodes Y1 and a sustain electrodes Z1 cross an address electrodes X1. A plurality of scanning electrodes Y1, . . . , Ym are drove in sequence, and a plurality of sustain electrodes Z1, . . . , Zm are drove in common. And a plurality of address electrodes X1, . . . , Xn are drove in division of even lines and odd lines.
In the above-described three electrodes AC normal discharge type PDP, it is the basic principle of each cell that first, address discharge is caused in a space between a the scanning electrode 12Y and the address electrode 12X in order to produce wall electric charge therein, second, sustain discharge is caused between the scanning electrode 12Y and the sustain electrode 12Z in order to make discharge gas a plasma, thereby producing an UV lights, and then the UV lights is made to excite phosphor in order to produce visible lights.
Such three electrodes AC normal discharge type PDP is drove in division of a plurality of sub-fields. And, in respective the plurality of sub-field periods, luminescence are produced several times, the number of which is proportional to weighted value of video data, thereby realizing contrast display. For example, in the case of displaying an image in 256 contrasts using 8 bits video data, one frame display time in respective discharge cells (for instance, a sixtieth second=about 16.7 msec) is divided into eight sub-fields SF1, . . . , SF8, as shown in FIG. 3.
Respective sub-fields SF1, . . . , SF8 is divided again into a reset period, an address period, and a sustain period, and then weighted values are allowed to the sustain period at the rate of 1:2:4:8:, . . . , 128. In this case, the reset period is a period for initializing a discharge cell, the address period is a period for causing an alternative address discharge in accordance with the logic value of video data, and the sustain period is a period for sustaining the discharge in the discharge cell where the address discharge is caused. The reset period and the address period are equivalently allowed in respective sub-field periods, but respective sustain periods are allowed at the rate of 1:2:4:8:16:32:64:128.
Therefore, 256 contrasts, each of which is different from 0 to 255, can be realized in one frame by properly selecting ON/OFF sub-fields. For Example, in the case of 1 contrast, only period of first sub-field, that is, period of SF1 is used. And, in the case of 100 contrast, only periods of third, sixth, and seventh sub-fields SF3, SF6, SF7 are used, and in the case of 256 contrast, periods of all sub-fields are used.
FIG. 4 is a diagram showing driving waveform of a conventional PDP in the case of using lamp waveform reset pulse in reset periods of all sub-fields in one frame.
As shown in FIG. 4, a reset pulse RP is applied to a scanning electrode Y in a reset period RPD of all sub-fields SF1, . . . , SF8. The reset pulse RP has a lamp waveform where a voltage increases in Set-up and a voltage decreases in Set-down. Because of reset discharge caused in Set-up, wall electric charges are formed at the upper dielectric layer 14. Then, decreasing voltage in Set-down erase unnecessary charge particles partially, so that wall electric charge decrease to the state for next address discharge without fault discharge.
To decrease the wall electric charge, a positive DC voltage Vs is applied to the sustain electrode Z in Set-down of the reset pulse RP. Because the reset pulse RP is applied in gradual decrease against this positive DC voltage Vs, the scanning electrode Y becomes relatively negative in comparison with the sustain electrode Z, that is, the polarity thereof reverses, thereby decreasing wall electric charges which are produced in Set-up.
In an address period APD, scan pulse SP is applied to the scanning electrode Y and data pulse CDP is applied to the address electrode X at the same time, thereby causing an address discharge. This address discharge produces a wall electric charge, and then the wall electric charge is sustained while the other discharge cells are addressed.
By applying triggering pulse TP to the scanning electrode Y in the initial point of sustain period SPD, sustain discharge is caused in discharge cells where wall electric charges are fully formed in the address period APD. Then, sustain pulses SUSPz and SUSPy are applied to the sustain electrode Z and the scanning electrode Y alternately, thereby sustaining the sustain discharge in sustain period SPD.
In an erasing period EPD following such sustain period SPD, by applying an erasing pulse to the sustain electrode Z, the sustained discharge is stopped. The erasing pulse EP is a lamp waveform having small size of luminescence, or has narrow pulse width such as about 1 us. As a result of short erase discharge due to such erase pulse EP, electric charges are erased, thereby stopping the discharge.
However, because the reset discharge caused in reset periods of all sub-fields in one frame has no connection with cell selection, there is a disadvantage of contrast reduction
To compensate such disadvantage resulting from the formation where all sub-fields include reset period, Japanese Laid-Open Patent Publication No. 2000-242224 discloses a technology that one field period has sub-fields SF1, . . . , SF8 each of which has reset period, address period, and sustain period, and a part of reset operation in reset periods of SF2, . . . , SF8 excluding SF1 is simultaneously made with the sustain operation of sustain period of previous sub-field, thereby decreasing reset time and discharge.
But, because reset period is not completely erased in this related art, there is a disadvantage that contrast is not improved greatly.